Best Evidence: VBAC or Repeat C-Section

Best evidence:
When making important maternity decisions, women should have
information from the best available research about the safety and
effectiveness of different choices. In general, we can be most
confident about results of systematic reviews that summarize randomized
controlled trials (or RCTs, a type of study).

Unfortunately,
for many decisions we must rely on less definitive research; and many
important questions even in the case of widely used drugs, tests and
procedures have hardly been studied at all. Although this situation is
discouraging, an awareness of weak or missing evidence can help you
make informed choices about care.

This page presents results of recent systematic reviews and other studies that can help women compare risks of planned vaginal birth after cesarean (VBAC)
and of planned c-section (see references at end of page). While more
high-quality studies are needed, a large body of research already
exists and sheds light on these questions for those who need guidance
now.

When deciding whether to plan a VBAC or a repeat
cesarean, it is important to understand the full range of risks to you
and your baby. This means comparing the short- and long-term risks of
cesarean surgery and risks of accumulating cesarean surgery scars to
mothers and babies on the one hand, to the risk that the uterine scar
will give way (uterine rupture) and lead to problems and a few risks that are worse for vaginal birth generally.

Even
if you do not plan to have more children, you should be aware of risks
of multiple cesarean scars to future pregnancies and babies. Many women
change their mind and decide to become pregnant again or continue with
unplanned pregnancies.

If
you do not have a clear and compelling need for a cesarean in the
present pregnancy, having a VBAC rather than a repeat c-section is
likely to be:

safer for you in this pregnancy

far safer for you and your babies in any future pregnancies

When
thinking about the health and safety of your baby in the present pregnancy, there
are trade-offs to consider: VBAC has some advantages, and a repeat
c-section has others. You can learn more below.

See details about scar-related effects after the following summary lists.

Despite limitations of the best available research, the following conclusions seem clear:

Scar giving way: The scar is more likely to give way during
a VBAC labor than in a repeat c-section; for most women (exceptions
noted below), the added risk of the scar giving way is about 4.2 in
every 1,000 VBAC labors. In other words, nearly 238 women would need
to experience the risks involved with repeat c-section to prevent one uterine rupture during a VBAC labor.

Death of baby: While the scar giving way poses a threat to
the baby, the added risk that the baby will die from a problem with the
scar during a VBAC labor, compared with women planning repeat
c-sections, is about 1.9 in every 10,000 VBAC labors. In other words,
over 5,200 women would need to experience the risks involved with repeat
c-sections to prevent the death of 1 baby due to uterine rupture.

Hysterectomy in mother: If the scar gives way, some women have an urgent hysterectomy
(removal of the uterus). However, cesareans also increase risk for urgent hysterectomy, and women who plan a VBAC are not more likely to experience an unplanned hysterectomy than women planning repeat c-section.

Multiple scars in uterus: As the number of c-section scars increases, the risk for experiencing several serious problems increases for women and fetuses in future pregnancies and births. These include:

scar rupture in a subsequent labor

ectopic pregnancy: the embryo develops outside the uterus

placenta previa: the placenta grows over the cervix, the opening to the uterus

placental abruption: the placenta separates from the uterus before the baby is born

placenta accreta the placenta grows abnormally into or even through the uterus.

The following factors do not increase risk of the scar giving way during labor:

type of uterine scar not known

low vertical uterine incision for prior c-section (may have been used if c-section was performed earlier in pregnancy before growth in lower part of the uterus)

baby estimated to be large, and to weigh more than 4,000 grams (8 pounds, 13 ounces)

pregnancy goes past 40 weeks, and labor is not induced

The following factors are associated with a low risk of the scar giving way, but too few cases have been studied to know the true risk:

twin pregnancy: uterine rupture does not appear to be more common in twin VBAC labors compared with singleton VBAC labors

use of external cephalic version: turning a baby who is positioned buttocks- or feet-first (breech) to head-first position by manipulating the woman's belly does not seem to cause or be associated with uterine rupture

When weighing planned VBAC
versus planned c-section, the focus is often on potential problems with
the uterine scar in labor in the present pregnancy. But this results in an incomplete picture. Women and their caregivers should consider all of the risks that differ between vaginal birth and cesarean section. Some of these are short-term risks like infection and bleeding while others are longer-term risks, including problems in future pregnancies. Summarized here are some of the many extra risks associated with cesarean surgery. The next question reviews advantages of cesarean birth. (In Best Evidence: C-Section, you can find a detailed comparison of risks of cesarean and vaginal birth, including how likely these problems are to occur.)

As
you consider these, keep in mind that on average, 3 out of 4 women who
labor after a c-section will give birth vaginally with care that
encourages and supports VBAC (and fewer than 1 in 100 will experience
the scar giving way). Even in cases where women are told they have a low chance of having a VBAC, if given the chance many or even most give birth vaginally.

Physical problems for mothers: Compared with vaginal birth,
cesarean section increases a woman's risk for a number of physical
problems. These range from less common but potentially life-threatening
problems, including hemorrhage (severe bleeding), blood clots, and bowel obstruction (due to scarring and adhesions
from the surgery), to much more common problems such as longer-lasting
and more severe pain and infection. Even after recovery from surgery,
scarring and adhesion tissue increase risk for ongoing pelvic pain and for twisted bowel.

Hospital stays: If a woman has a c-section, she is more likely to stay in the hospital longer and to be re-hospitalized.

Emotional well-being: A woman who has a c-section may be at
greater risk for poorer overall mental health and some emotional
problems. She is also more likely to rate her birth experience poorer
than a woman who has had a vaginal birth.

Mother-baby relationship: A woman who has a c-section is
more likely to have less early contact with her baby and initial
negative feelings about her baby.

Breastfeeding: Recovery from surgery poses challenges for
getting breastfeeding under way, and a baby who was born by c-section
is less likely to be breastfed and get the benefits of breastfeeding.

Impact on babies: Babies born by c-section are more likely to:

be cut during the surgery (usually minor)

have breathing difficulties around the time of birth

experience asthma in childhood and in adulthood.

Impact on any future babies: A cesarean section in this
pregnancy increases risk for babies in future pregnancies. Some
research finds that babies who develop in a scarred uterus are more
likely to:

C-section
offers advantages in a few areas, primarily during the recovery period
after birth. Some practices used with vaginal birth, such as episiotomy,
are associated with pelvic floor problems. It is wrong to conclude at
this time that vaginal birth itself causes such problems. See the
Pregnancy Topic Preventing Pelvic Floor Dysfunction.

A woman who has a vaginal birth is more likely to:

have a painful vaginal area in the weeks after birth

leak urine (urinary incontinence) (about 3 women per hundred still have a problem 1 year after birth)

leak gas, or more rarely, feces (bowel incontinence) (about 3 women per hundred still have a problem 1 year after birth)

Babies born vaginally have been shown to be at higher risk for a nerve injury affecting the shoulder, arm, or hand (brachial plexus injury) (usually temporary).

What are some ways that a planned c-section may differ from an unplanned c-section?

A
planned c-section offers some advantages over an unplanned c-section
that occurs during labor. For example, there is a lower
risk of surgical injuries and of infections. The emotional impact of a
cesarean that is planned in advance appears to be similar to or
only somewhat worse than a vaginal birth. By contrast, unplanned cesareans
can take a greater emotional toll. In addition, a woman planning repeat
cesarean surgery would almost certainly be less likely to experience
difficulty breastfeeding if she had breastfed before or to have
negative feelings for her baby compared with a first-time mother having
an unplanned cesarean. Nonetheless, a planned cesarean still involves
the risks associated with major surgery. And both planned and unplanned
cesareans result in a uterine scar, which increases risk for serious
concerns for mothers and babies in future pregnancies, and for adhesion-relation problems in mothers at any time.

MORE DETAILED INFORMATION ABOUT SCAR-RELATED RISKS NOTED ABOVE

Best research suggests that an extra 4.2 women experience a ruptured uterus
in every 1,000 VBAC labors, compared with planned c-section
deliveries. Thus, about 238 women would need to experience surgical
birth to prevent one instance of uterine rupture during VBAC
labors. While the scar giving way usually requires an urgent cesarean,
loss of the baby is much less common (see next paragraph). Added likelihood for a woman with a known low-transverse (horizontal) scar: MODERATE for scar rupture compared with planned repeat c-section.

Best
research suggests that about 1.9 more babies die due to problems with
the scar in every 10,000 VBAC labors, compared with planned c-section
deliveries. Thus, about 5,200 women would need to experience risks of
surgical birth to prevent the death of 1 baby from scar problems during
VBAC. Added likelihood for a woman with a known low-transverse (horizontal) scar: LOW for death of the baby around the time of birth compared with repeat c-section.

low vertical uterine incision at prior c-section (may have been used if c-section took place earlier in pregnancy before growth in lower part of the uterus)

baby estimated to be large, weighing over 4,000 grams (8 lb 13 oz) or

pregnancy extends past 40 weeks?

Some
caregivers recommend planned repeat c-section with these factors on the
grounds that VBAC is riskier, but the research does not support that
belief. More detailed information on these issues can be found in Options: VBAC or Repeat C-Section. No
added likelihood for scar rupture in a woman with unknown type of
uterine scar, prior low vertical uterine incision, baby estimated to
weigh more than 4,000 grams, or pregnancy extending past 40 weeks, in
comparison with women planning VBAC without these factors.

While
studies have not found an excess incidence of scar rupture in these
situations, not enough women have been studied to rule out an increase.
More detailed information on these issues can be found in Options: VBAC or Repeat C-Section. No
currently known added likelihood for scar rupture in a woman with a
twin pregnancy or a woman experiencing external version, in comparison
with women planning VBAC without these factors.

Although hysterectomy (surgical removal of the uterus) can result from uterine rupture in a VBAC labor, most studies find an excess of hysterectomies among women planning repeat c-section. However, this could be because those studies may have included cases where the c-section was planned for reasons that could increase the risk of complications during surgery such as the placenta overlaying the cervix (placenta previa). A study that took care to exclude women having planned repeat cesareans for medical reasons found no difference in the percentages of women having hysterectomies. No apparent added likelihood for hysterectomy for a woman planning VBAC compared with a woman planning repeat c-section.

The likelihood of the following problems grows as the number of previous cesareans (and c-section scars) grows:

placenta previa: a woman whose uterus has a cesarean
scar is more likely than a woman with an unscarred uterus to have a
future placenta attach near or over the opening to her cervix;
this increases her risk for serious bleeding, shock, blood transfusion,
blood clots, planned or emergency delivery, emergency removal of her
uterus (hysterectomy), placenta accreta (see next), and other complications. Added likelihood for a woman with a previous cesarean: MODERATE for placenta previa in a future pregnancy after having one cesarean; HIGH for placenta previa in a future pregnancy after having more than one cesarean

placenta accreta: a woman whose uterus has a cesarean
scar is more likely than a woman with an unscarred uterus to have a
future placenta grow through the uterine lining and into or through the
muscle of the uterus; this increases her risk for uterine rupture (see below), serious bleeding, shock, blood transfusion, emergency surgery, emergency removal of her uterus (hysterectomy), and other complications. Added likelihood for a woman with at least one previous cesarean: MODERATE for placenta accreta in a future pregnancy, with increasing risk as the number of previous cesareans grows

rupture of the uterus: a woman whose uterus has a
cesarean scar is more likely than a woman with an unscarred uterus to
have the uterine wall give way in a future pregnancy or labor,
especially at the site of the scar; this increases her risk for severe
bleeding, shock, blood transfusion, blood clots, planned or emergency
cesarean delivery, emergency removal of the uterus (hysterectomy), and other complications; whether a woman plans a repeat cesarean or a VBAC (vaginal birth after cesarean), she is at greater risk for a ruptured uterus than a woman with no previous cesarean. Added likelihood for a woman with a previous cesarean: MODERATE for rupture of the uterus, with increasing risk for two or more cesareans

For some scar-related adverse effects in future pregnancies, we did not find research to clarify whether risks increase as the number of previous cesareans increases.

The following risks for mothers are worse after one cesarean
and may or may not grow as the number of c-section scars grow:
fertility problems, ectopic pregnancy (pregnancy growing outside the uterus), and placental abruption
(placenta detaches before birth).

The following risks for babies are
worse after one cesarean and may or may not grow as the number of
c-section scars grows: being born too early (preterm), being born too small (low birthweight), having a physical abnormality or injury to the brain or spinal cord, and dying before birth (stillbirth) or shortly after birth.

Scarring and adhesion tissue often increase as the the number of cesareans increases, creating greater and greater challenges for any future surgical procedures in the area. We did not find information to clarify whether the likelihood of the following adhesion-related problems grows as the number of cesareans grows: ongoing pelvic pain and risk for twisted and blocked bowel in women.

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